1. Field of the Invention
The present invention relates to a digital video (or versatile) disk reproducing apparatus, and in particular, to a method of automatically controlling a bandwidth of a waveform equalizer to minimize a data error rate during pulse detection.
2. Description of the Related Art
A digital video (or versatile) disc (hereinafter referred to as a DVD), which is a recording medium for a digital moving picture, can record a digital MEPG2 (Moving Picture Experts Group 2) signal indicative of the digital moving picture which is over 2 hours in duration. A general DVD reproducing apparatus for reproducing the audio and video signals recorded on the DVD has a construction as shown in FIG. 1.
Referring to FIG. 1, a DVD 10 mounted on a driving axle of a spindle motor 12 rotates at a constant speed. A pickup device 14 contained in a deck (not shown) irradiates a laser beam onto the DVD 10 and receives a reflected beam from the DVD 10 to read data recorded on the DVD 10. Further, the pickup device 14 controls rotation and loading of the DVD 10 and transfer of a pickup head (not shown). An RF (Radio Frequency) amplifier 16 amplifies the signal picked up by the pickup device 14 and shapes the amplified signal. A digital signal processor (DSP) 18 demodulates (16-8 demodulation) the signal output from the RF amplifier 16, and performs data PLL (base Locked Loop) by means of synchronous detection, descrambling, error detection, error correction, and track buffer control function.
Specifically, the DSP 18 includes a 16-8 demodulator (not shown) and an error correction circuit (not shown). The 16-8 demodulator detects synchronization for the input data and 16-8 demodulates the input data to store it into a memory (i.e., track buffer) 20. The error correction circuit reads the data stored in the track buffer 20 to correct errors of the read data, and then stores the error-corrected data back into the track buffer 20. Further, the DSP 18 searches the data stored in the track buffer 20 for ID (identification) data representative of a disc position, to provide the ID data to a system controller 22, and descrambles the remaining data to store it into the track buffer 20. At the request of an MPEG2 video decoder 30, the DSP 18 reads and transfers the descrambled data stored in the track buffer 20 to the MPEG2 video decoder 30. The system controller 22 controls an overall operation of the DVD reproducing apparatus. A pickup servo controller 24 performs focusing servo, tracking servo and pickup transfer servo, under the control of the system controller 22. A spindle servo controller 26 controls a rotation number of the spindle motor 12, such that a period of the longest or shortest pit of an EFM (Eight-to-Fourteen Modulated) signal read from the DVD 10 should become a prescribed value. A demultiplexer 28 demultiplexes the signal output from the DSP 18, to transfer a video signal to the MPEG2 video decoder 30 and an audio signal to an AC3/MPEG audio decoder 34, respectively. The video and audio output signals from the video decoder 30 and the audio decoder 34 are transferred to a monitor and a speaker via an NTSC encoder 32 and a digital-to-analog converter (DAC) 36, respectively. A keypad 38 (user interface means) includes a plurality of keys with which the user inputs data or commands. A display 40 displays thereon various state information concerning reproduction of the DVD 10.
The RF amplifier 16 of the DVD reproducing apparatus generally includes an adder (not shown) and a waveform equalizer (not shown). In operation, since the signal picked up by the pickup device 14 is divided into four signals for the focusing servo and grouped into two groups, these signals undergo an I-V (current-to-voltage) conversion and are then converted into a signal of a single group. The EFM signal amplified and shaped at the adder is a 3-14T pulse train, so that the reproduced signal is susceptible to having an error due to interference between adjacent waveforms. Accordingly, there has long been a demand for a device which can reduce bandwidth of the waveform equalizer as narrow as possible in order to minimize the interference and as a result, reduce the error rate during pulse detection. Conventionally, a jitter meter was used to reduce the bandwidth of the waveform equalizer. That is, the conventional apparatus measured the EFM signal equalized at the waveform equalizer by using the jitter meter, to determine the bandwidth of the waveform equalizer. Accordingly, the bandwidth of the waveform equalizer is determined passively, so that the bandwidth is inaccurately determined, thereby increasing the data error rate undesirably.